Can anyone send me or post a schematic, or describe, the heater hose and valve plumbing for an 04 GTO?

I tried to figure out what goes where on the valve by flowing water thru it and it just doesn't make sense. I have alldata and it doesn't show a schematic of the flow. Actually I'm not that impressed by alldata, but that's a whole nother story.

Might be a dumb question considering I figured out how to get the engine and trans into a Volvo, but I'm stumped.

Pretty sure the smaller is the pressure side and the larger fitting is the return, although on mine I just tapped them with a 3/8 & 1/2 NPT tap and plugged them and I havent had any problems although if it is discussed here you will get a bout 50/50 in favor of plugging those lines or not plugging those lines, but if you plan on using them for a heater the small one is the pressure side.

I noticed you didn't get any responses specific to your question, so I'll give it a shot. Though I don't know about the GTO specifically, I did come up against the heater valve issue when I did mine. Perhaps your confusion (as was mine) stems from a couple of areas 1.) The heater valve is a bypass type since coolant must continue to circulate through the heater hoses and back to the pump. Some argue it's not necessary, but that's how the stock system was designed. 2.) The heater control valve (on the f-body) is normally open (to circulate through the heater core). When vacuum is applied, the valve closes and re-circulates the coolant back to the water pump. As such, the heater control valve requires a constant vacuum signal to keep it closed, then when the heater is needed, the vacuum signal must be turned off so as to open the valve sending hot water to the heater core.

I suspect many people simply ignore the re-circulating system and plumb a traditional heater valve in the traditional in-line manner.

I noticed you didn't get any responses specific to your question, so I'll give it a shot. Though I don't know about the GTO specifically, I did come up against the heater valve issue when I did mine. Perhaps your confusion (as was mine) stems from a couple of areas 1.) The heater valve is a bypass type since coolant must continue to circulate through the heater hoses and back to the pump. Some argue it's not necessary, but that's how the stock system was designed. 2.) The heater control valve (on the f-body) is normally open (to circulate through the heater core). When vacuum is applied, the valve closes and re-circulates the coolant back to the water pump. As such, the heater control valve requires a constant vacuum signal to keep it closed, then when the heater is needed, the vacuum signal must be turned off so as to open the valve sending hot water to the heater core.

I suspect many people simply ignore the re-circulating system and plumb a traditional heater valve in the traditional in-line manner.

Andy1

Andy you're right.
No one has provided the specifics I need, it's recirculating system, and there's plenty of debate whether recirc is necessary, but if GM spent the money to put in a 4-way valve there must be a reason.

The GTO is vacuum to close the flow to the heater core from what I can tell.

My problem is I can't get enough flow thru a sink faucet to see what goes where when the valve is actuated and not. Blowing thru it doesn't cut it because there's too much internal leakage, and my outdoor hose is buried in what this year appears to be permafrost.

I'm sure it'll be one of those "duh" moments when I see what the schematic is like, but right now I'm thinking there must be another hose or something because I just can't figure out the in's and out's of the 4 port valve.

Andy you're right.
No one has provided the specifics I need, it's recirculating system, and there's plenty of debate whether recirc is necessary, but if GM spent the money to put in a 4-way valve there must be a reason.

The GTO is vacuum to close the flow to the heater core from what I can tell.

My problem is I can't get enough flow thru a sink faucet to see what goes where when the valve is actuated and not. Blowing thru it doesn't cut it because there's too much internal leakage, and my outdoor hose is buried in what this year appears to be permafrost.

I'm sure it'll be one of those "duh" moments when I see what the schematic is like, but right now I'm thinking there must be another hose or something because I just can't figure out the in's and out's of the 4 port valve.

You might take a second look at the valve logic; that's what I had to do in order to realize it's not what I thought at first. Perhaps it doesn't translate to the GTO valve senario, but in the case of the Camaro heater control valve it's vacuum off to run the hot water to the heater core. Try your water test with that in mind to see if it works; I simply blew ito the ports to determine the logic. A kind person on this forum took some photos, ran his motor, and initiated the heater control lever in his Camaro and indeed the vacuum to the valve was vented and the vacuum pot lever went to normally open. My car is in paint, so I don't have the system running yet to confirm this 100%, but that's how I'm proceeding.

With engine on and heater dash control off/cold, vacumm is feed to the control valve.. the valve would be pulled closed and water will be rerouted back to the pump from the pump. (right smal port to right large port)

When the dash control is turned on/hot, the vacumn is turned off, the vavle will open and route water to the small inlet on heater core. (right Small port to left small port), Water exiting the heater core (larger port).. well then be routed through the control valve and back to the pump (left Side large port to the right side large port)

I think the one that is pictured above is for a pickup/SUV. The GTO one has 5/8" ports for all 4 hookups. I used one of these on the '68 Camaro, and to solve the 3/4" to 5/8" issue, I just forced a 5/8" hose on. Off the top of my head, I can't remember which way the floe goes with the vacuum on or off. Here's a diagram for a Holden, don't mind the fact that it's not an LS motor, or a LHD car, for that matter. This should be the exact part you have.

The valve in the photo is 4-Seasons #74781 with 5/8" hot side, and 3/4" cold side (return). That works out for the Fbody,Vette, and truck/SUV water pump heater hoses AFAIK; I'm not sure about the GTO, but I know it's valve uses 5/8" all around.